1. Field of the Invention
The present invention relates to a dielectric recording medium for recording information in a dielectric material or reproducing it, and a method of and an apparatus for producing the dielectric recording medium.
2. Description of the Related Art
Recently, many types of dielectric materials and piezoelectric materials have been developed, and most of them are used for ultrasonic elements, optical elements, a memory, and the like. In accordance with the fact, a method of measuring a spontaneous polarization distribution of the dielectric material and local anisotropy of the piezoelectric material has been developed Also, by using this technique, techniques of recording and reproducing information in the dielectric material have been developed.
As a method of producing a dielectric thin film used as a storage medium for recording and reproducing information, the following is known a method of using a vacuum coating apparatus, such as a MOCVD (Metal Organic Chemical Vapor Deposition) method, a sputtering method, and a laser ablation method; and a method of applying and sintering a MO (Metal Organic) material and the like, such as a melt ferroelectric crystal growing method such as a liquid phase epitaxial method, a sol-gel method, and a dipping method. The dielectric thin films prepared by these methods are used as the small capacitor of the storage medium or the nonvolatile storage medium of a ferroelectric memory.
On the other hand, a super high-density recording and/or reproducing system in which the dielectric (ferroelectric) thin film is used as a recording medium is proposed by the inventors of the present invention. This apparatus applies a voltage to a probe, which has a small spherical tip, to form a polarization domain and thus information is recorded. With respect to the reproduction of the information, using the function of a SNDM (Scanning Nonlinear Dielectric Microscopy) enables the record in and the reproduction from a domain on the order of nm. A ferroelectric substance as being the recording medium used for this kind of system needs to have an appropriate dielectric constant and an appropriate coercive electric field. Moreover, its polarization direction needs to be uniformly vertical to a recording surface in the domain on the order of nm, and also it needs to be extremely thin such as 1000 Å or less.
However, a conventional method of producing the dielectric thin film has difficulty in preparing the dielectric thin film which meets the conditions for the recording medium used with the above-described SNDM method.
For example, in the sol-gel method of applying and firing or sintering the MO material, it is possible to obtain the dielectric thin film inexpensively because it does not need a vacuum apparatus and the like. However, it is difficult to control the polarization direction, which is required as a prerequisite for a high-recording-density recording medium, and it is also difficult to uniformly form the thin film that is 1000 Å or less. This is because even if the film is uniform immediately after spin-coating, the thin film easily becomes porous by the decomposition and the removal of organic components during the subsequent firing process, and thus, it is not possible to control the generation of growth nuclei of the ferroelectric crystal with uniform size on the order of nm. Moreover, the growth of the crystal thin film by the conventional sol-gel method is generally epitaxial growth to a substrate crystal, and the control of the ferroelectric crystal orientation, i.e. the control of the polarization direction is not performed.